The first Global System for Mobile (GSM) communication networks were designed for voice services rather than for data services. When the use of GSM data services started, it soon became evident that the Circuit Switched (CS) bearer services were not well-suited for certain types of applications with a bursty nature. Therefore the new Packet Switched (PS) data transmission service GPRS (General Packet Radio Service) was developed for packet services. GPRS is a packet radio network utilizing the GSM network, and GPRS endeavours to optimize data packet transmission by means of GPRS protocol layers on the air interface between a mobile station (hereinafter also called a mobile terminal) and a GPRS network.
A GPRS mobile station (MS) can operate in one of three modes of operation, as described in 3GPP TS 23.060, “Service description; Stage 2,” Section 5.4.5. The three modes are Class-A Mode, Class-B Mode, and Class-C Mode. According to the Class-A mode of operation, the MS is attached to both GPRS as well as other GSM services, and therefore Class-A Mode corresponds to Dual Transfer Mode (DTM) Mode (hereinafter also called dual mode). The mobile user in Class-A Mode can make and/or receive calls on the two services simultaneously, for example having a normal GSM voice call and receiving GPRS data packets at the same time. According to the Class B mode of operation, the MS is attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time. According to the Class C mode of operation, the MS can only be attached either to the GSM network or the GPRS network; the selection is done manually and there are no simultaneous operations.
Based on the current standard (3GPP TS 44.018, “Radio Resource Control Protocol”), when the MS is in packet transfer mode and a CS connection (also referred to as a radio resource or RR connection) is needed, then all packet resources must first be aborted, then an RR connection is established, and finally packet resources may be requested. This process occurs, for example, when the MS initiates a call. This prior art system is illustrated in FIG. 1 (also see 3GPP TS 43.064, “Overall description of the GPRS radio interface; Stage 2”), which shows RR operating modes and transitions between Class-A (DTM supported) and Class-B. A Temporary Block Flow (TBF) Release moves the MS from the Packet Transfer Mode 106 into an Idle/Packet Idle state 104, after which the MS must then establish a dedicated RR connection 108 in order to then access dual transfer mode 102 that includes both packet transfer capability and RR capability. In other words, after the release of the packet transfer connection 106, the MS is in the packet idle mode 104 and must perform a complete acquisition of system information and ask for PS resources all over again, in order to get into the Dual Mode 102 via the dedicated CS mode 108.
FIG. 2 further illustrates how the system is currently working, according to the prior art. The four vertical lines represent portions or stages of the network. The line 202 represents the mobile station (MS), the line 204 represents the base station system (BSS), the line 206 represents the serving GPRS support node (SGSN), and the line 208 represents the mobile switching center (MSC). Either the MS or network can request a CS connection. In either case, the packet session 210 is aborted and the establishment of the CS connection is initiated. In FIG. 2, a network pages the MS for a CS connection. The MS releases packet resources and transfers to the packet idle mode 214 in which mode the MS asks for CS resources as specified in 3GPP TS 44.018, “Radio Resource Control Protocol.” When the MS has progressed to the dedicated mode 212, then the MS must request PS resources if PS resources are desired, by submitting a dual transfer mode (DTM) request as described in 3GPP TS 43.064, “Overall Description of the GPRS Radio Interface; Stage 2.”
The main problem with these prior art techniques is that the MS is not allowed to immediately enter a combined CS mode 212 and PS mode 216 (which together comprise a dual mode) until the MS has performed various time-consuming steps. Thus, the mobile station will be forced to idle its packet switching capabilities, while it sets up the circuit switching session 212.